1. Field of the Invention
The present invention relates to a process which makes it possible to obtain undrawn filaments based on polaymide (PA) with better output efficiency.
It also relates to polyamide-based undrawn modified yarns suitable for texturing by and drawing false-twist texturing.
2. Description of the Related Art
Undrawn polyamide-based yarns which are generally employed for the operation of drawing-texturing using false twist must have orientation and low crystallinity properties so as to orient the macromolecules better and then to crystallize and thus set the orientation during the drawing-texturing process without degrading or breaking the filaments during the thermal setting of the yarn.
In particular, it is known according to French patent application published under no. 2,274,710 to prepare PA yarns which can be employed directly in processes for drawing-texturing using false twist, by melt-spinning polyhexamethylmethylene adipamide, cooling, treatment in an atmosphere of water vapor and under pressure to obtain the desired yarn properties, and preferably a slight overdrawing of the yarns before winding. The latter is carried out at speeds which are generally between 270 and 4000 m/min.
To increase the spinning speed without substantially modifying the crystallinity and orientation properties of the undrawn POY yarns, it has also been proposed in European patent application published under no. 080,274 (A) to introduce into the molten PA polyethylene or polypropylene subsequently forming microfibrils in the filaments obtained.
However, the addition of polymer in the form of fine particles present disadvantages when carried out industrially: in particular, it requires a highly sophisticated technology for obtaining mixtures which have sufficient fineness and stability with time to permit reliable spinning without strand breakages. As a result, such a technique cannot be employed industrially.
It is also known to improve the output efficiency of unoriented PA yarns suitable for texturing using false twist, by introducing into the polymeric chains from 0.01 to 1 mol % of a branching agent such as bishexamethylenetriamine or trimesic acid or 4-aminomethyl-1,8-diaminooctane. However, such compounds modify the rheology of the polymer by increasing its viscoelasticity, with the result that spinning such copolymers becomes very tricky and present considerable risks of strand breakages.
Moreover, it is also known, according to French patent application published under no. 1,428,439, to prepare PA resin compositions containing silica in the form of particles of &lt;10 .mu.m of specific conductance &lt;5.times.10.sup.-4 mho/cm.
However, the use of such compositions relates to plastics applications.
It is also known, according to French patent no. 1,169,578 to prepare PA compositions for compression and injection moulding which have wider softening and melting ranges, making it possible to maintain a viscous flow and to avoid gels by incorporating into the PA inorganic fillers such as SiO.sub.2 with a particle size of 1 to 40 .mu.m.